Ultraviolet-curable resin material for pattern transfer and magnetic recording medium manufacturing method using the same

ABSTRACT

According to one embodiment, this invention uses an ultraviolet-curable resin material for pattern transfer containing 80 to 95 wt % of isobornyl acrylate, 1 to 20 wt % of trifunctional acrylate, and 0.5 to 6 wt % of a polymerization initiator.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2009-060930, filed Mar. 13, 2009, theentire contents of which are incorporated herein by reference.

BACKGROUND

1. Field

One embodiment of the present invention relates to a method ofmanufacturing a magnetic recording medium having discrete tracks on thesurface of a magnetic recording layer and, more particularly, to anultraviolet-curable resin material to be used when transferring adiscrete track shape.

2. Description of the Related Art

Recently, the nano-imprinting techniques are attracting attention invarious fields in order to further increase the density and accuracy.

For example, applications to semiconductors, optical elements, magneticrecording media, and the like are being examined.

As a magnetic recording medium, a discrete track medium is attractingattention. In this discrete track medium, magnetic interference betweenadjacent recording tracks is reduced by separating the adjacent tracksby grooves or guard bands made of a nonmagnetic material in order tofurther increase the density.

When manufacturing this discrete track medium, discrete track patternsof a magnetic layer can be formed by applying the nano-imprintingtechnique by using a stamper. When magnetic layer patterns correspondingto servo area signals are formed together with recording track patternsby imprinting, it is possible to obviate the servo track writing steprequired in the manufacture of the conventional magnetic recordingmedia. This leads to a cost reduction.

As the process of forming discrete track patterns as described above, aprocess of transferring resist patterns from an Ni stamper by, e.g.,high-pressure imprinting or thermal imprinting has been used.Unfortunately, this process is unsuitable for mass-production becausethe life of the Ni stamper is short. Also, when the data density isincreased to make tracks finer, resist patterns cannot be welltransferred.

From the foregoing, the use of optical nano-imprinting is attractingattention as another nano-imprinting technique.

To transfer patterns onto a resist on a discrete track medium by usingoptical nano-imprinting, a resin stamper is first duplicated from an Nistamper (mother stamper) by injection molding, and bonded in a vacuum toan uncured ultraviolet-curable resin layer to be used as a resist. Thismethod is found to be able to reduce the cost and suitable formicropatterning.

The characteristics required of the ultraviolet-curable resin to betransferred onto the above-mentioned discrete track medium are theproperty of coating onto the medium, the viscosity, the curing property,the property of separation from the resin stamper, the resistanceagainst etching for processing transferred patterns, and the cureshrinkage. The thickness of the ultraviolet-curable resin must besufficient for imprinting with respect to the height of thethree-dimensional structure of transfer patterns. For later processingsteps, however, the amount of residue of the ultraviolet-curable resinafter imprinting is preferably small. Therefore, the coating filmthickness of the ultraviolet-curable resin layer is desirably 60 nm orless.

An example of the ultraviolet-curable resin for radical polymerizationis an ultraviolet-curable resin obtained by mixing an initiator, anoligomer having a vinyl (acryloyl) group, and a monomer (see, e.g.,non-patent reference 1). However, when an oligomer is mixed in anultraviolet-curable resin, the viscosity increases, and this makes itdifficult to decrease the coating film thickness to 60 nm or less.

Also, as disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2008-19292,an example of the ultraviolet-curable resin for nano-imprinting is anultraviolet-curable resin to which a surfactant is added to improve thecoating property and the property of separation. If the amount ofsurfactant is too large, however, curing inhibition readily occurs, thecuring time tends to prolong, or the magnetic recording medium oftendeteriorates.

In addition, since the coating film thickness must be very small, i.e.,60 nm or less, film thickness control is difficult to perform unless theviscosity of the ultraviolet-curable resin is 15 cP or less.

If a monofunctional monomer alone is cured, the curing property of thefilm degrades. On the other hand, if the functional order is increased,the film cures, but the cure shrinkage readily increases.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

A general architecture that implements the various feature of theinvention will now be described with reference to the drawings. Thedrawings and the associated descriptions are provided to illustrateembodiments of the invention and not to limit the scope of theinvention.

FIGS. 1A, 1B, 1C, and 1D are views showing a pattern transfer method tobe used in the present invention;

FIG. 2 is a view showing a magnetic recording/reproduction apparatus forperforming recording and reproduction on a magnetic recording medium;

FIGS. 3A, 3B, 3C, 3D, 3E, 3F, 3G, 3H, 3I, 3J, and 3K are views showingan example of a discrete magnetic recording medium manufacturing method;and

FIG. 4 is a view showing an outline of the arrangement of a transferpattern sample evaluation apparatus.

DETAILED DESCRIPTION

Various embodiments according to the invention will be describedhereinafter with reference to the accompanying drawings. In general,according to one embodiment of the invention, an ultraviolet-curableresin material for pattern transfer is provided, which containsisobornyl acrylate represented by formula (I) below, trifunctionalacrylate, and a polymerization initiator. The composition is that thecontent of isobornyl acrylate is 80 to 95 wt %, that of thetrifunctional acrylate is 1 to 20 wt %, and that of the polymerizationinitiator is 0.5 to 6 wt %.

In the present invention, the viscosity of the ultraviolet-curable resinmaterial is adjusted to 15 cP or less by mixing isobornyl acrylate, thetrifunctional acrylate, and the polymerization initiator at apredetermined mixing ratio, so a coating film having a small uniformthickness of 60 nm or less can be formed. This makes it possible toreduce the residue of the imprinted ultraviolet-curable resin. Also, theultraviolet-curable resin material for pattern transfer having theabove-mentioned composition are superior in ultraviolet curing property,property of separation after curing, etching resistance, and cureshrinkage. When using this ultraviolet-curable resin material forpattern transfer, therefore, accurate pattern transfer can be performedfrom a stamper.

Isobornyl acrylate has a relatively low viscosity of 9 cP and arelatively high glass transition point Tg. Also, isobornyl acrylate hasa high etching resistance because it has an alicyclic structure. When amaterial containing two components, i.e., this isobornyl acrylate and apolymerization initiator was used as the ultraviolet-curable resinmaterial for pattern transfer, the hardness of the cured film wasinsufficient. This similarly happened when a monofunctional monomer, abifunctional monomer, and isobornyl acrylate were combined. When atrifunctional monomer was combined, the hardness of the cured film wassufficient while the etching resistance remained high. The viscosityoften increases when using a polyfunctional monomer larger than atrifunctional monomer.

Also, a magnetic recording medium manufacturing method includes bonding,in a vacuum, the surface of a magnetic recording layer of a magneticrecording medium including a data area and servo area, and athree-dimensional pattern surface of a resin stamper, with a coatinglayer of an uncured ultraviolet-curable resin material for patterntransfer being interposed between them,

curing the coating layer of the uncured ultraviolet-curable resinmaterial by irradiating the coating layer with ultraviolet rays,

separating the resin stamper to form, on one surface of the magneticrecording medium, a cured ultraviolet-curable resin material layer ontowhich a three-dimensional pattern is transferred, and

performing dry etching by using the cured ultraviolet-curable resinmaterial layer as a mask, thereby forming a three-dimensional pattern onthe surface of the magnetic recording layer,

wherein the ultraviolet-curable resin material for pattern transfercontains 80 to 95 wt % of isobornyl acrylate, 1 to 20 wt % ortrifunctional acrylate, and 0.5 to 6 wt % of a polymerization initiator.

In addition to the acrylates and polymerization initiator describedabove, an additive such as an adhesive can be mixed at a ratio of 1 wt %or less in the ultraviolet-curable resin material for pattern transferof the present invention.

The ultraviolet-curable resin material for pattern transfer of thepresent invention can have a viscosity of 9 to 15 cP at 25° C.

As the trifunctional acrylate, it is possible to use, e.g.,

trimethylolpropane triacrylate,

trimethylolpropane PO-modified triacrylate

-   -   (number of propoxy groups [POs]: 2, 3, 4, 6),

trimethylolpropane EO-modified triacrylate

-   -   (number of ethoxy groups [EOs]: 3, 6, 9, 15, 20),

tris(2-hydroxyethyl)isocyanurate triacrylate,

pentaerythritol triacrylate,

pentaerythritol EO-modified triacrylate,

EO-modified glycerin triacrylate,

propoxylated (3) glyceryl triacrylate,

highly propoxylated (5.5) glyceryl triacrylate,

trisacryloyloxyethyl phosphate, and

ε-caprolactone-modified tris(acryloxyethyl)isocyanurate.

As the polymerization initiator, it is possible to use, e.g., analkylphenone-based photopolymerization initiator, acylphosphineoxide-based polymerization initiator, titanocene-based polymerizationinitiator, oxime ester-based photopolymerization initiator, or oximeester acetate-based photopolymerization initiator.

Practical examples of the above-mentioned polymerization initiators are

2,2-dimethoxy-1,2-diphenylethane-1-on (Irgacure 651 manufactured by CibaSpecialty Chemicals),

1-hydroxy-cyclohexyl-phenyl-ketone (Irgacure 184 manufactured by CibaSpecialty Chemicals), and

2-hydroxy-2-methyl-1-phenyl-propane-1-on (Darocur 1173 manufactured byCiba Specialty Chemicals).

Other examples are Irgacure 2959, Irgacure 127, Irgacure 907, Irgacure369, Irgacure 379, Darocur TPO, Irgacure 819, Irgacure 784, IrgacureOXE01, Irgacure OXE02, and Irgacure 754 (all are manufactured by CibaSpecialty Chemicals).

It is possible to select an optimum polymerization initiator inaccordance with the wavelength of a lamp for use in UV irradiation.

As the lamp for use in UV irradiation, it is possible to use, e.g., ahigh-pressure mercury lamp, metal halide lamp, or xenon flash lamp.

An outline of a pattern transfer method to be used in the presentinvention will be explained below with reference to FIGS. 1A to 1D.

FIGS. 1A to 1D illustrate the transfer of patterns onto one surface of amedium substrate. As shown in FIG. 1A, a medium substrate 51 is set on aspinner 41. As shown in FIG. 1B, while the medium substrate 51 is spuntogether with the spinner 41, an ultraviolet-curable resin (2P resin) isdropped from a dispenser 42 and spin-coated. As shown in FIG. 1C, in avacuum chamber 81, one surface of the magnetic recording medium 51 and apattern surface of a transparent stamper 71 are bonded in a vacuum witha 2P resin layer (not shown) being interposed between them. As shown inFIG. 1D, the 2P resin layer is cured by emitting UV radiation from a UVlight source 43 through the transparent stamper 71 at atmosphericpressure. After the step shown in FIG. 1D, the transparent stamper 71 isseparated.

Examples of a magnetic disk substrate usable in the present inventionare a glass substrate, an Al-based alloy substrate, a ceramic substrate,a carbon substrate, an Si single-crystal substrate having an oxidizedsurface, and a substrate obtained by forming an NiP layer on the surfaceof any of these substrates. As the glass substrate, amorphous glass orcrystallized glass can be used. Examples of the amorphous glass are sodalime glass and alumino silicate glass. An example of the crystallizedglass is lithium-based crystallized glass. As the ceramic substrate, itis possible to use a sintered product mainly containing aluminum oxide,aluminum nitride, or silicon nitride, or a material formed byfiber-reinforcing the sintered product. Plating or sputtering is used toform the NiP layer on the substrate surface.

When manufacturing a perpendicular magnetic recording medium, aso-called perpendicular double-layered medium can be formed by forming aperpendicular magnetic recording layer on a soft magnetic underlayer(SUL) on a substrate. The soft magnetic underlayer of the perpendiculardouble-layered medium passes a recording magnetic field from a recordingmagnetic pole, and returns the recording magnetic field to a return yokeplaced near the recording magnetic pole. That is, the soft magneticunderlayer performs a part of the function of a recording head; the softmagnetic underlayer applies a steep perpendicular magnetic field to therecording layer, thereby increasing the recording efficiency.

An example of the soft magnetic underlayer usable in the presentinvention is a high-k material containing at least one of Fe, Ni, andCo. Examples of the material are FeCo-based alloys such as FeCo andFeCoV, FeNi-based alloys such as FeNi, FeNiMo, FeNiCr, and FeNiSi,FeAl-based and FeSi-based alloys such as FeAl, FeAlSi, FeAlSiCr,FeAlSiTiRu, and FeAlO, FeTa-based alloys such as FeTa, FeTaC, and FeTaN,and FeZr-based alloys such as FeZrN.

As the soft magnetic underlayer, it is also possible to use a materialhaving a microcrystal structure such as FeAlO, FeMgO, FeTaN, or FeZrNcontaining 60 at % or more of Fe, or a material having a granularstructure in which fine crystal grains are dispersed in a matrix.

As another material of the soft magnetic underlayer, it is possible touse a Co alloy containing Co and at least one of Zr, Hf, Nb, Ta, Ti, andY. The content of Co can be 80 at % or more. An amorphous layer isreadily formed when a film of the Co alloy is formed by sputtering. Theamorphous soft magnetic material has none of magnetocrystallineanisotropy, a crystal defect, and a grain boundary, and hence has superbsoft magnetism. It is also possible to reduce the noise of the medium byusing the amorphous soft magnetic material. Favorable examples of theamorphous soft magnetic material are CoZr-based, CoZrNb-based, andCoZrTa-based alloys.

Another underlayer may also be formed below the soft magnetic underlayerin order to improve the crystallinity of the soft magnetic underlayer orimprove the adhesion to the substrate. As the underlayer material, it ispossible to use Ti, Ta, W, Cr, Pt, an alloy containing any of thesematerials, or an oxide or nitride of any of these materials.

An interlayer made of a nonmagnetic material can be formed between thesoft magnetic underlayer and perpendicular magnetic recording layer. Theinterlayer interrupts the exchange coupling interaction between the softmagnetic underlayer and recording layer, and controls the crystallinityof the recording layer. As the interlayer material, it is possible touse Ru, Pt, Pd, W, Ti, Ta, Cr, Si, an alloy containing any of thesematerials, or an oxide or nitride of any of these materials.

To prevent spike noise, it is possible to divide the soft magneticunderlayer into a plurality of layers, and antiferromagnetically couplethese layers with 0.5- to 1.5-nm-thick Ru films being sandwiched betweenthem. Also, the soft magnetic layer can be coupled by exchange couplingwith a hard magnetic film having in-plane anisotropy such as CoCrPt,SmCo, or FePt, or a pinning layer made of an antiferromagnetic materialsuch as IrMn or PtMn. To control the exchange coupling force, a magneticlayer such as a Co layer or a nonmagnetic layer such as a Pt layer canbe stacked above and below the Ru layer.

As the perpendicular magnetic recording layer usable in the presentinvention, it is possible to use a material mainly containing Co,containing at least Pt, containing Cr as needed, and further containingan oxide (e.g., silicon oxide or titanium oxide). In this perpendicularmagnetic recording layer, the magnetic crystal grains can form a pillarstructure. In the perpendicular magnetic recording layer having thisstructure, the orientation and crystallinity of the magnetic crystalgrains are favorable. As a consequence, a signal-to-noise ratio (SNR)suitable for high-density recording can be obtained. The amount of oxideis important to obtain the above structure. The content of the oxide canbe 3 to 12 mol %, and can also be 5 to 10 mol %, with respect to thetotal amount of Co, Pt, and Cr. When the content of the oxide in theperpendicular magnetic recording layer falls within the above range, theoxide deposits around the magnetic grains, so the magnetic grains can beisolated and downsized. If the content of the oxide exceeds the aboverange, the oxide remains in the magnetic grains and deteriorates theorientation and crystallinity of the magnetic grains. Furthermore, theoxide deposits above and below the magnetic grains. Consequently, thepillar structure in which the magnetic grains vertically extend throughthe perpendicular magnetic recording layer is often not formed. On theother hand, if the content of the oxide is less than the above range,the magnetic grains are insufficiently isolated and downsized. As aresult, noise increases in recording and reproduction, and this oftenmakes it impossible to obtain a signal-to-noise ratio (SNR) suited tohigh-density recording.

The content of Pt in the perpendicular magnetic recording layer can be10 to 25 at %. When the Pt content falls within the above range, auniaxial magnetic anisotropy constant Ku necessary for the perpendicularmagnetic recording layer is obtained. In addition, the crystallinity andorientation of the magnetic grains improve. Consequently, a thermaldecay characteristic and recording/reproduction characteristic suited tohigh-density recording are obtained. If the Pt content exceeds the aboverange, a layer having the fcc structure is formed in the magneticgrains, and the crystallinity and orientation may deteriorate. On theother hand, if the Pt content is less than the above range, it is oftenimpossible to obtain Ku, i.e., a thermal decay characteristic suitablefor high-density recording.

The content of Cr in the perpendicular magnetic recording layer can be 0to 16 at %, and can also be 10 to 14 at %. When the Cr content fallswithin the above range, it is possible to maintain high magnetizationwithout decreasing the uniaxial magnetic anisotropy constant Ku of themagnetic grains. Consequently, a recording/reproduction characteristicsuited to high-density recording and a sufficient thermal decaycharacteristic are obtained. If the Cr content exceeds the above range,the thermal decay characteristic worsens because Ku of the magneticgrains decreases. In addition, the crystallinity and orientation of themagnetic grains worsen. As a consequence, the recording/reproductioncharacteristic tends to worsen.

The perpendicular magnetic recording layer can contain one or moreadditive elements selected from B, Ta, Mo, Cu, Nd, W, Nb, Sm, Tb, Ru,and Re, in addition to Co, Pt, Cr, and the oxide. These additiveelements can promote the downsizing of the magnetic grains, or improvethe crystallinity and orientation of the magnetic grains. This makes itpossible to obtain a recording/reproduction characteristic and thermaldecay characteristic more suitable for high-density recording. The totalcontent of these additive elements can be 8 at % or less. If the totalcontent exceeds 8 at %, a phase other than the hcp phase is formed inthe magnetic grains, and this disturbs the crystallinity and orientationof the magnetic grains. As a result, it is often impossible to obtain arecording/reproduction characteristic and thermal decay characteristicsuited to high-density recording.

Other examples of the material of the perpendicular magnetic recordinglayer are a CoPt-based alloy, a CoCr-based alloy, a CoPtCr-based alloy,CoPtO, CoPtCrO, CoPtSi, and CoPtCrSi. As the perpendicular magneticrecording layer, it is also possible to use a multilayered filmcontaining Co and an alloy mainly containing at least one elementselected from the group consisting of Pt, Pd, Rh, and Ru. It is furtherpossible to use a multilayered film such as CoCr/PtCr, CoB/PdB, orCoO/RhO obtained by adding Cr, B, or O to each layer of the formermultilayered film.

The thickness of the perpendicular magnetic recording layer can be 5 to60 nm, and can also be 10 to 40 nm. A perpendicular magnetic recordinglayer having a thickness falling within this range is suited to a highrecording density. If the thickness of the perpendicular magneticrecording layer is less than 5 nm, the reproduction output becomes toolow, so the noise component often becomes higher than the reproductionoutput. On the other hand, if the thickness of the perpendicularmagnetic recording layer exceeds 40 nm, the reproduction output becomestoo high and tends to distort the waveform. The coercive force of theperpendicular magnetic recording layer can be 237,000 A/m (3,000 Oe) ormore. If the coercive force is less than 237,000 A/m (3,000 Oe), thethermal decay resistance tends to decrease. The perpendicular squarenessratio of the perpendicular magnetic recording layer can be 0.8 or more.If the perpendicular squareness ratio is less than 0.8, the thermaldecay resistance often decreases.

A protective layer can be formed on the perpendicular magnetic recordinglayer.

The protective layer prevents the corrosion of the perpendicularmagnetic recording layer, and also prevents damages to the mediumsurface when a magnetic head comes in contact with the medium. Examplesof the material of the protective layer are materials containing C,SiO₂, and ZrO₂. The thickness of the protective layer can be 1 to 10 nm.When the thickness of the protective layer falls within the above range,the distance between the head and medium can be decreased. This issuitable for high-density recording.

The surface of the perpendicular magnetic recording medium can be coatedwith a lubricant, e.g., perfluoropolyether, alcohol fluoride, orfluorinated carboxylic acid.

FIG. 2 is a view showing a magnetic recording/reproduction apparatus forperforming recording and reproduction on the magnetic recording medium.

This magnetic recording apparatus includes, in a housing 61, a magneticrecording medium 62, a spindle motor 63 for rotating the magneticrecording medium 62, a head slider 64 including a recording/reproductionhead, a head suspension assembly (a suspension 65 and actuator arm 66)for supporting the head slider 64, a voice coil motor 67, and a circuitboard.

The magnetic recording medium 62 is attached to and rotated by thespindle motor 63, and various digital data are recorded by theperpendicular magnetic recording method. The magnetic head incorporatedinto the head slider 64 is a so-called composite head, and includes awrite head having a single-pole structure and a read head using a GMRfilm or TMR film. The suspension 65 is held at one end of the actuatorarm 66, and supports the head slider 64 so as to oppose it to therecording surface of the magnetic recording medium 62. The actuator arm66 is attached to a pivot 68. The voice coil motor 67 is formed as anactuator at the other end of the actuator arm 64. The voice coil motor67 drives the head suspension assembly to position the magnetic head inan arbitrary radial position of the magnetic recording medium 62. Thecircuit board includes a head IC, and generates, e.g., a voice coilmotor driving signal, and control signals for controlling read and writeby the magnetic head.

An address signal and the like can be reproduced from the processedmagnetic recording medium by using this magnetic disk apparatus.

A magnetic disk in which the track density was 325 kTPI (tracks perinch, equivalent to a track pitch of 78 nm) in a data zone having aradius of 9 to 22 mm was manufactured by using the method of the presentinvention.

To manufacture the magnetic disk having this servo area, imprinting isperformed using a stamper having three-dimensional patternscorresponding to magnetic layer patterns on the magnetic disk. Note thatthe surface of the three-dimensional patterns of the magnetic layerformed by imprinting and subsequent processing may also be planarized byburying a nonmagnetic material in recesses.

A method of manufacturing the magnetic disk of this embodiment will beexplained below.

First, a stamper was manufactured.

An Si wafer having a diameter of 6 inches was prepared as a substrate ofa master as a template of the stamper. On the other hand, resistZEP-520A available from Zeon was diluted to half with anisole, and thesolution was filtered through a 0.05-μm filter. The Si wafer wasspin-coated with the resist solution and prebaked at 200° C. for 3minutes, thereby forming a resist layer about 50 nm thick.

An electron beam lithography system having a ZrO/W thermal fieldemission type electron gun emitter was used to directly write desiredpatterns on the resist onto the Si wafer at an acceleration voltage of50 kV. This lithography was performed using a signal source thatsynchronously generates signals for forming servo patterns, burstpatterns, address patterns, and track patterns, signals to be suppliedto a stage driving system (a so-called X-θ stage driving systemincluding a moving mechanism having a moving axis in at least onedirection and a rotating mechanism) of the lithography system, and anelectron beam deflection control signal. During the lithography, thestage was rotated at a constant linear velocity (CLV) of 500 mm/s, andmoved in the radial direction as well. Also, concentric track areas werewritten by deflecting the electron beam for every rotation. Note thatthe feeding speed was 7.8 nm per rotation, and one track (equivalent toone address bit width) was formed by ten rotations.

The resist was developed by dipping the Si wafer in ZED-N50 (availablefrom Zeon) for 90 seconds. After that, the Si wafer was rinsed as it wasdipped in ZMD-B (available from Zeon) for 90 seconds, and dried by airblow, thereby manufacturing a resist master (not shown).

A conductive film made of Ni was formed on the resist master bysputtering. More specifically, pure nickel was used as a target. After achamber was evacuated to 8×10⁻³ Pa, the pressure was adjusted to 1 Pa bysupplying argon gas, and sputtering was performed in the chamber for 40seconds by applying a DC power of 400 W, thereby forming a conductivefilm about 10 nm thick.

The resist master having this conductive film was dipped in a nickelsulfamate plating solution (NS-160 available from Showa ChemicalIndustry), and Ni electroforming was performed for 90 minutes, therebyforming an electroformed film about 300 μm thick. The electroformingbath conditions were as follows.

Electroforming Bath Conditions

Nickel sulfamate: 600 g/L

Boric acid: 40 g/L

Surfactant (sodium lauryl sulfate): 0.15 g/L

Solution temperature: 55° C.

pH: 4.0

Current density: 20 A/dm²

The electroformed film and conductive film were separated together withthe resist residue from the resist master. The resist residue wasremoved by oxygen plasma ashing. More specifically, plasma ashing wasperformed for 20 minutes by applying a power of 100 W in a chamber inwhich the pressure was adjusted to 4 Pa by supplying oxygen gas at 100mL/min.

As shown in FIG. 3A, a father stamper 1 including the conductive filmand electroformed film as described above was obtained. After that,electroforming was further performed to duplicate a mother stamper 2 asshown in FIG. 3B. An injection molding stamper was obtained by removingunnecessary portions of the mother stamper 2 by a metal blade.

As shown in FIG. 3C, a resin stamper 3 was duplicated from the motherstamper 2 by using an injection molding apparatus manufactured byToshiba Machine. As the molding material, cyclic olefin polymer Zeonor1060R available from Zeon was used. However, polycarbonate materialAD5503 available from Teijin Chemicals may also be used.

Then, a magnetic disk was manufactured.

A magnetic recording layer was formed by sputtering on a disk substratemade of doughnut-like glass 1.8 inches in diameter shown in FIG. 3G. A3-nm-thick metal mask layer was stacked on this magnetic recordinglayer. Examples of a metal usable as the metal mask layer are Ag, Al,Au, C, Cr, Cu, Ni, Pt, Pd, Ru, Si, Ta, Ti, Zn, and alloys (e.g., CrTi,CoB, CoPt, CoZrNb, NiTa, NiW, Cr—N, SiC, and TiO_(x)) containing thesemetals. When using Si or Cu among these metals, the property ofseparation from the resin stamper and the processability tend toimprove. The film thickness of the metal mask layer is determined by theprocessability, and can be as small as possible. In this embodiment, a3-nm-thick Cu layer was stacked on the magnetic recording layer.

After a surface protection layer 6 was formed on a magnetic recordinglayer 5 as shown in FIG. 31, a resist 7 made of an ultraviolet-curableresin material was formed by spin coating at a rotational speed of10,000 rpm.

As shown in FIG. 3C, the resin stamper 3 was bonded to theultraviolet-curable resin resist 7 on the surface of the disk substrateby vacuum bonding, and the resin was cured by ultraviolet irradiation.After that, the resin stamper 3 was separated as shown in FIG. 3D.

In a three-dimensional pattern formation process performed byultraviolet imprinting, the resist residue remains on the bottoms ofpattern recesses.

Then, the resist residue on the bottoms of pattern recesses was removedby RIE using oxygen gas. As shown in FIG. 3E, the magnetic recordinglayer was etched by Ar ion milling by using the patterns of the resist 7as masks. Subsequently, as shown in FIG. 3F, the resist patterns wereremoved by oxygen RIE. In addition, a carbon protective layer (notshown) was formed on the entire surface. After that, the manufacturedmagnetic disk was coated with a lubricant.

In the magnetic disk medium described above, the magnetic recordinglayer was etched to the bottom in a portion where no resist mask wasformed. However, it is also possible to stop Ar ion milling halfway toobtain a medium having projections and recesses. Alternatively, it ispossible to obtain a medium by imprinting a stamper onto a resist on asubstrate without initially forming any magnetic layer, making thesubstrate shape three-dimensional by etching or the like, and thenforming a magnetic film. Furthermore, in any medium including theabove-mentioned media, the grooves may also be filled with a certainnonmagnetic material.

A resin stamper was duplicated by the above-mentioned method by usingone Ni stamper, and ultraviolet-curable resin resist mask transfer wasperformed. 100 magnetic disks were duplicated for eachultraviolet-curable resin.

A resin stamper was duplicated by the above-mentioned method by usingone Ni stamper, and ultraviolet-curable resin resist mask transfer wasperformed.

The ultraviolet-curable resin was evaluated for five items, i.e., theviscosity, curing property, property of separation, Ar sputter etchingrate, and repeatable run-out (RRO).

The viscosity of the ultraviolet-curable resin was measured using arotary viscometer (TVE-22LT manufactured by Toki Sangyo).

The curing property was evaluated after transfer by wiping up the resinwith cloth wetted by ethanol. The evaluation was ⊚ when there was nochange, ◯ when there were two or more fine scratches, Δ when there werethree or more scratches, and x when the wiped portion entirely peeledoff.

The property of separation was evaluated as ◯ when no 2P resin remainedon the resin stamper after separation, Δ when the 2P resin slightlyremained, and x when the 2P resin remained in a wide area.

The Ar sputter etching rate was measured by performing plasma etching inan Ar ambient at an Ar pressure of 1 Pa and an RF power of 100 W for 200seconds by using 51A Sputtering Equipment manufactured by ShubauraMechatronics. Before and after the etching, the film thickness of theultraviolet-curable resin was measured by using Dektak 6M Stylus SurfaceProfiler manufactured by Ulvac. The etching rate was calculated bynormalizing the difference between the film thicknesses before and afterthe etching by the etching time. The higher the etching resistance, thehigher the processability when using the ultraviolet-curable resin.Therefore, the etching rate can be made as low as possible. For example,the etching rate was set at 0.25 nm/s or less as a reference.

The RRO is an effective means for checking the cure strain of theultraviolet-curable resin. As the strain increases, the roundness oftransferred patterns decreases, and the RRO tends to degrade. Anevaluation apparatus for use in this evaluation is DDU-1000 manufacturedby Pulstec.

First, an ultraviolet-curable resin transfer pattern sample was preparedfor RRO evaluation. A glass plate having an inner diameter of 12.01 mm,an outer diameter of 32.00 mm, and a thickness of 0.6 mm was spin-coatedwith KBM503 available from Shin-Etsu Chemical. In the same manner as ina normal magnetic recording medium transfer/separation process, thecoating film was coated with an ultraviolet-curable resin, patterntransfer was performed using a resin stamper, and the resin stamper wasseparated from the glass plate.

The RRO was evaluated by applying a laser from the side opposite to thetransfer side of the ultraviolet-curable resin. The RRO is favorablewhen it is 1 nm or less.

An apparatus for checking the RRO of three-dimensional patterns will beexplained below.

FIG. 4 is a block diagram showing an outline of the arrangement of theRRO evaluation apparatus for checking the RRO.

A semiconductor laser source 120 is used as a light source. Thewavelength of the exit light is in, e.g., the violet wavelength bandwithin the range of 400 to 410 nm. Exit light 110 from the semiconductorlaser source 120 is collimated into parallel light by a collimator lens121, and this parallel light enters an objective lens 124 through apolarizing beam splitter 122 and λ/4 plate 123. After that, the light istransmitted through a substrate of sample S, and concentrated on asubstrate surface in which grooves are formed. The numerical aperture(to be referred to as the NA hereinafter) of the laser changes inaccordance with the medium as an object. For example, the NA is about0.5 to 0.7 for this sample when using an evaluation method by which thelaser is transmitted through the interior of a 0.6-mm-thick transferpattern sample. On the other hand, when using a sample made of anon-transmitting material or when playing back the surface of a sample,it is possible to adjust the NA to 0.85 or more, or insert an aberrationcorrecting plate equivalent to a 0.6-mm-thick resin material between thelaser and sample. Reflected light 111 from an information recordinglayer of the transfer pattern sample is transmitted through thesubstrate of transfer pattern sample S again, transmitted through theobjective lens 124 and λ/4 plate 123, and reflected by the polarizingbeam splitter 122. After that, the reflected light 111 enters aphotodetector 127 through a condenser lens 125.

A light-receiving unit of the photodetector 127 is normally divided intoa plurality of portions, and each light-receiving portion outputs anelectric current corresponding to the light intensity. The outputelectric current is converted into a voltage by an I/V amplifier(current-voltage converter) (not shown), and the voltage is input to anarithmetic circuit 140. The arithmetic circuit 140 performs anarithmetic operation on the input voltage signal, thereby generating atilt error signal, HF signal, focusing error signal, and tracking errorsignal. The tilt error signal is used to perform tilt control. The HFsignal is used to reproduce information recorded on optical disk D. Thefocusing error signal is used to perform focusing control. The trackingerror signal is used to perform tracking control.

The objective lens 124 can be driven in the vertical direction, discradial direction, and tilt direction (radial and/or tangentialdirection) by an actuator 128, and is controlled to trace informationtracks on transfer pattern sample S by a servo driver 150.

Note that in this evaluation apparatus, the wavelength of thesemiconductor laser is in the range of 400 to 410 nm as an example.However, the present invention is not limited to this, and thewavelength can also be shorter. Note also that in this evaluationapparatus, the groove track pitch of the transfer pattern sample can bemade smaller than, e.g., 0.4 μm. When the semiconductor laser has a longwavelength, the groove track pitch of the transfer pattern sample mustbe larger than 0.4 μm. The track pitch can be determined by the laserspot diameter. When performing tracking by using the push-pull method ofthe evaluation apparatus, the groove track pitch of the transfer patternsample can be 0.5 to 1.2 times the laser spot diameter. The laser spotdiameter can be represented by λ/NA. For example, when the laserwavelength is 405 nm and the NA is 0.65, the groove track pitch can be0.31 to 0.75 μm. Also, when using, e.g., a fixed laser having awavelength of 355 nm and an NA of 0.85, the laser spot diameter is 0.42μm, so a minimum track pitch can be 0.2 μm. If the track pitch is toolarge, a dummy area expands, and the laser spot diameter of theevaluation apparatus tends to increase, so coarse evaluation is oftenperformed on a data area. Therefore, the track pitch can be as small aspossible. On the other hand, a laser wavelength shorter than 355 nm isimpractical because it is difficult to handle. Accordingly, the lowerlimit of the groove track pitch can be 0.2 μm.

The transfer pattern sample of the present invention can be played backby using the RRO evaluation apparatus as described above. In thisembodiment, Pulstec DDU-1000 was used. The laser wavelength was 405 nm,and the NA was 0.65.

The method of evaluating the RRO of a transfer pattern sample will nowbe explained.

A transfer pattern sample was set in the above-mentioned evaluationapparatus and rotated at a linear velocity of 1.2 m/s. Note that thelinear velocity tends to decrease as the frequency rises (the servo gaincharacteristic) because the apparatus has the tracking characteristic.When the linear velocity is a lowest velocity equal to or higher thanthe minimum rotational speed of the spindle motor, therefore, ahigh-order component of the RRO can be checked more accurately byamplifying the displacement amount of the order. In this evaluationapparatus, one rotation of the disk is converted into a frequency as arotational frequency, and the eccentric order is represented by thisrotational frequency.

A laser was emitted, and the tilt and offset were adjusted such that thedifference signal (push-pull signal) was maximum, thereby performingtracking. The frequency of the push-pull signal after tracking wasanalyzed using an FFT analyzer (CF-5210 manufactured by Ono Sokki).

Then, the peak-to-peak value of the same push-pull signal was checkedwhile tracking was turned off and only focusing was adjusted. Thispeak-to-peak voltage value is equivalent to a half-track pitchdisplacement amount. The displacement amount was calculated by dividingthe voltage value at each frequency measured by the FFT analyzer by thepeak-to-peak voltage value. Note that the measurement conditions of theFFT analyzer were that data obtained by measuring one track 100 timesand averaging the results was regarded as one measurement, and a maximumvalue of the results of five measurements performed by changing tracksin a dummy area was regarded as the displacement amount. Thiscalculation result was used as the RRO of the transfer pattern sample inthe present invention. Assuming that the rotational frequency of thetransfer pattern sample was the first-order displacement amount as areference, attention was particularly given to the 15th- to 40th-orderdisplacement amounts. When the order is less than 15th, an error readilyoccurs owing to a position where a transfer pattern sample is placed.Also, a certain stable displacement amount is obtained withoutperforming measurement exceeding the 40th order.

Although a transfer pattern sample by which the ratio of the land to thegroove was 1:1 was used in the above example, the present invention isnot limited to this. The characteristics of the apparatus for checkingthe RRO characteristic make tracking impossible to perform if PP/SUM<0.1where PP/SUM is a value obtained by normalizing an amplitude (p−p) of apush-pull signal PP by a voltage value (p−G) of a sum signal SUM.Accordingly, it is possible to select a land-to-groove ratio at whichtracking can be performed by preventing this.

Examples 1-12 & Comparative Examples 1-11

Magnetic recording media were manufactured by transferring patterns ontomagnetic recording layers by the above method by usingultraviolet-curable resins A to Y.

Table 1 shows the contents of ultraviolet-curable resins A to Y, andTable 2 shows the results.

Symbols in Table 1 will be explained below.

IBOA: Isobornyl acrylate

TITA: Tris(2-hydroxyethyl)isocyanurate triacrylate

IRGACURE369: 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1

EGTA3: Ethoxylated (3) glyceryl triacrylate

wherein l+m+n=3 in formular (4) above

EGTA9: Ethoxylated (9) glyceryl triacrylate

l+m+n=9 in formula (4) above

EGTA20: Ethoxylated (20) glyceryl triacrylate

l+m+n=20 in formula (4) above

TMPTA: Trimethylolpropane triacrylate

TMPTA-3EO: Ethoxylated (3) trimethylolpropane triacrylate

wherein l+m+n=3 in formula (6) above

PUHA: Polyurethane hexaacrylate

wherein n=25

TCDMA: Tricyclodecanedimethanol diacrylate

PEA: 2-phenoxyethyl acrylate

PBFA: Propoxylated bisphenol A glycidyl etherified acrylate

DTMPTA: Ditrimethylolpropane tetraacrylate

Ultraviolet-curable resins A to K and Y were found to beultraviolet-curable resins suitably used to transfer patterns onto amagnetic recording medium in respect of all of the viscosity, propertyof separation, curing property, film thickness, etching rate, and RRO.

Among others, C, D, F, G, J, and Y were particularly superior in etchingrate.

When using trifunctional acrylates having the same skeleton, the etchingrate decreased as an ethoxy group was increased, so the etchingresistance increased.

A, C, G, and Y were particularly superior in curing property.

For the film thickness, Y having a lowest viscosity was best, and A, D,F, G, and J were also good.

On the other hand, L, N, O, R, U, and X were bad in curing property. Inparticular, X containing no polymerization initiator did not cure atall. M and N were inferior in etching resistance, and N, P, Q, R, and Scaused large cure shrinkage because they were bad in RRO.

The above results indicate that the ultraviolet-curable resin containing80 to 95 wt % of isobornyl acrylate, 1 to 20 wt % of trifunctionalacrylate, and 0.5 to 6 wt % of a polymerization initiator are superiorin ultraviolet curing property, property of separation after curing,etching resistance, and cure shrinkage. The above results alsodemonstrate that accurate pattern transfer can be performed from astamper when using the ultraviolet-curable resin material for patterntransfer as described above.

Furthermore, the contents of the IBOA, trifunctional acrylate, andpolymerization initiator can particularly be 85 to 93 wt %, 6 to 10 wt%, and 1 to 5 wt %, respectively.

It was possible to obtain favorable characteristics when forming DTRmedia by using good ultraviolet-curable resins and checking therecording/reproduction characteristics.

Note that although Irgacure 369 was used as the polymerization initiatorin the examples, but it is naturally possible to appropriately selectany polymerization initiator in accordance with the affinity to the UVlamp or acrylate.

TABLE 1 Trifunctional Polymerization Resin Acrylate acrylate initiatorExample 1 A IBOA 90 wt % TITA(6 wt %) IRGACURE369 4 wt % Example 2 BIBOA 90 wt % EGTA3(6 wt %) IRGACURE369 4 wt % Example 3 C IBOA 90 wt %EGTA9(6 wt %) IRGACURE369 4 wt % Example 4 D IBOA 90 wt % EGTA20(6 wt %)IRGACURE369 4 wt % Example 5 E IBOA 90 wt % TMPTA(6 wt %) IRGACURE369 4wt % Example 6 F IBOA 90 wt % TMPTA-3EO(6 wt %) IRGACURE369 4 wt %Example 7 G IBOA 85 wt % TMPTA-3EO(10 wt %) IRGACURE369 5 wt % Example 8H IBOA 80 wt % TMPTA-3EO(15 wt %) IRGACURE369 5 wt % Example 9 I IBOA 90wt % TMPTA-3EO(8 wt %) IRGACURE369 2 wt % Example 10 J IBOA 95 wt %TMPTA-3EO(4 wt %) IRGACURE369 1 wt % Example 11 K IBOA 80 wt %TMPTA-3EO(18 wt %) IRGACURE369 2 wt % Comparative Example 1 L IBOA 98 wt% TMPTA-3EO(1.5 wt %) IRGACURE369 0.5 wt % Comparative Example 2 M IBOA84 wt % PUHA 10 wt % IRGACURE369 6 wt % Comparative Example 3 N IBOA 90wt % TCDMA 6 wt % IRGACURE369 4 wt % Comparative Example 4 O PEA 92 wt %PBFA 5 wt % IRGACURE369 3 wt % Comparative Example 5 P IBOA 90 wt %DTMPTA 6 wt % IRGACURE369 4 wt % Comparative Example 6 Q IBOA 77 wt %TMPTA-3EO(21 wt %) IRGACURE369 2 wt % Comparative Example 7 R IBOA 77 wt%/ TMPTA-3EO 0.8 wt % IRGACURE369 2.2 wt % PEA 20 wt % ComparativeExample 8 S IBOA 78 wt % TMPTA-3EO 21 wt % IRGACURE369 1 wt %Comparative Example 9 T IBOA TMPTA-3EO(10 wt %) IRGACURE369 6.5 wt %83.5 wt % Comparative Example 10 U IBOA 88 wt % TMPTA-3EO(12.6 wt %)IRGACURE369 0.4 wt % Comparative Example 11 X IBOA 88 wt % TMPTA-3EO(13wt %) IRGACURE369 0 wt % Example 12 Y IBOA 93 wt % TMPTA-3EO(6 wt %)IRGACURE369 1 wt %

TABLE 2 Viscosity Property of Curing Film RRO Resin (CP) separationproperty thickness (nm/sec) (nm) Example 1 A 11 ◯ ⊚ 44 0.24 ◯ 0.4Example 2 B 10 ◯ ◯ 53 0.20 ◯ 0.7 Example 3 C 10 ◯ ⊚ 48 0.12 ◯ 0.5Example 4 D 10 ◯ ◯ 42 0.12 ◯ 0.7 Example 5 E 10 ◯ ◯ 47 0.16 ◯ 0.6Example 6 F 10 ◯ ◯ 43 0.12 ◯ 0.5 Example 7 G 13 ◯ ⊚ 44 0.11 ◯  0.75Example 8 H 14 ◯ ◯ 58 0.13 ◯ 0.9 Example 9 I 11.5 ◯ ◯ 52 0.14 ◯ 0.7Example 10 J 9.5 ◯ ◯ 37 0.10 ◯ 0.5 Example 11 K 15 ◯ ◯ 59 0.16 ◯ 1.0Comparative L 9 ◯ X 32 0.12 ◯ Immeasurable Example 1 Comparative M 13 ◯Δ 54 0.26 X 0.4 Example 2 Comparative N 10 ◯ X 47 0.27 X 1.2 Example 3Comparative O 11 ◯ X 52 0.12 ◯ 0.8 Example 4 Comparative P 16 ◯ ⊚ 620.18 ◯ 1.5 Example 5 Comparative Q 19 ◯ ⊚ 67 0.17 ◯ 1.1 Example 6Comparative R 9.3 Δ X 45 0.14 ◯ 1.2 Example 7 Comparative S 18 Δ ⊚ 680.20 ◯ 1.2 Example 8 Comparative T 16 ◯ Δ 61 0.21 ◯ 0.8 Example 9Comparative U 10 ◯ X 48 0.16 ◯ Immeasurable Example 10 Comparative X 9.5◯ X Immeasurable Immeasurable Immeasurable Example 11 Example 12 Y 9.3 ◯⊚ 36 0.10 ◯ 0.4

While certain embodiments of the inventions have been described, theseembodiments have been presented by way of example only, and are notintended to limit the scope of the inventions. Indeed, the novel methodsand systems described herein may be embodied in a variety of otherforms; furthermore, various omissions, substitutions and changes in theform of the methods and systems described herein may be made withoutdeparting from the spirit of the inventions. The accompanying claims andtheir equivalents are intended to cover such forms or modifications aswould fall within the scope and spirit of the inventions.

1. An ultraviolet-curable resin material for pattern transfercomprising: 80 to 95 wt % of an isobornyl acrylate; 1 to 18 wt % of atrifunctional acrylate; and 0.5 to 6 wt % of a polymerization initiator.2. The material of claim 1, wherein the material has a viscosity of 9 to15 cP at 25° C.
 3. The ultraviolet-curable resin material of claim 1,wherein the isobornyl acrylate comprises 85 to 93 wt %; thetrifunctional acrylate comprises 6 to 10 wt %; and the polymerizationinitiator comprises 1 to 5 wt %.
 4. The ultraviolet-curable resinmaterial of claim 1, wherein the trifunctional acrylate is selected fromthe group consisting of trimethylolpropane triacrylate,trimethylolpropane PO-modified triacrylate, trimethylolpropaneEO-modified triacrylate, tris(2-hydroxyethyl)isocyanurate triacrylate,pentaerythritol triacrylate, pentaerythritol EO-modified triacrylate,EO-modified glycerin triacrylate, propoxylated (3) glyceryl triacrylate,highly propoxylated (5.5) glyceryl triacrylate, trisacryloyloxyethylphosphate, and ε-caprolactone-modified tris(acryloxyethyl)isocyanurate.5. The ultraviolet-curable resin material of claim 1, wherein thepolymerization initiator is selected from the group consisting of analkylphenone-based photopolymerization initiator, acylphosphineoxide-based polymerization initiator, titanocene-based polymerizationinitiator, oxime ester-based photopolymerization initiator, or oximeester acetate-based photopolymerization initiator.
 6. Theultraviolet-curable resin material of claim 1 further comprising anadhesive additive of 1 wt % or less.
 7. The ultraviolet-curable resinmaterial of claim 1, wherein: the trifunctional acrylate is ethoxylated(3) trimethylolpropane triacrylate; and the polymerization initiator is2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1.
 8. Theultraviolet-curable resin material of claim 7, wherein: the isobornylacrylate comprises about 93 wt %; the ethoxylated (3) trimethylolpropanetriacrylate comprises about 6 wt %; and the2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1 comprisesabout 1 wt %.
 9. The ultraviolet-curable resin material of claim 7,wherein: the isobornyl acrylate comprises about 85 wt %; the ethoxylated(3) trimethylolpropane triacrylate comprises about 10 wt %; and the2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1 comprisesabout 5 wt %.
 10. A magnetic recording medium manufacturing methodcomprising: contacting, under a vacuum, a surface of a magneticrecording layer of a magnetic recording medium comprising a data areaand a servo area, and a three-dimensional pattern surface of a resinstamper, with a coating layer of an uncured ultraviolet-curable resinmaterial for pattern transfer comprising 80 to 95 wt % of isobornylacrylate, 1 to 18 wt % of trifunctional acrylate, and 0.5 to 6 wt % of apolymerization initiator interposed between the surface of the magneticrecording layer and the three-dimensional pattern surface; curing thecoating layer of the uncured ultraviolet-curable resin material byultraviolet irradiation; separating the resin stamper to form, on onesurface of the magnetic recording medium, a cured ultraviolet-curableresin material layer comprising a transferred three-dimensional pattern;and dry etching with the cured ultraviolet-curable resin material layeras a mask, thereby forming a three-dimensional pattern on the surface ofthe magnetic recording layer.
 11. The method of claim 10, wherein theuncured ultraviolet-curable resin material for pattern transfer has aviscosity of 9 to 15 cP at 25° C.
 12. The method of claim 10, whereinthe cured ultraviolet-curable resin material layer comprises a thicknessof 60 nm or less.
 13. The method of claim 10, wherein the curedultraviolet-curable resin material layer comprises a thickness between10 nm and 40 nm.
 14. The method of claim 10, wherein the uncuredultraviolet-curable resin material comprises: 85 to 93 wt % of theisobornyl acrylate; 6 to 10 wt % of the trifunctional acrylate; and 1 to5 wt % of the polymerization initiator.
 15. The method of claim 10,wherein: the trifunctional acrylate is ethoxylated (3)trimethylolpropane triacrylate; and the polymerization initiator is2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1.
 16. Themethod of claim 10, wherein: the isobornyl acrylate comprises about 90wt %; the trifunctional acrylate is tris(2-hydroxyethyl)isocyanuratetriacrylate comprising about 6 wt %; and the polymerization initiator is2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1 comprisingabout 4 wt %.
 17. The method of claim 10, wherein: the isobornylacrylate comprises about 93 wt %; the trifunctional acrylate isethoxylated (3) trimethylolpropane triacrylate comprising about 6 wt %;and the polymerization initiator is2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1 comprisingabout 1 wt %.
 18. The method of claim 10, wherein: the isobornylacrylate comprises about 85 wt %; the trifunctional acrylate isethoxylated (3) trimethylolpropane triacrylate comprising about 10 wt %;and the polymerization initiator is2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1 comprisingabout 5 wt %.
 19. The method of claim 10, wherein the trifunctionalacrylate is selected from the group consisting of trimethylolpropanetriacrylate, trimethylolpropane PO-modified triacrylate,trimethylolpropane EO-modified triacrylate,tris(2-hydroxyethyl)isocyanurate triacrylate, pentaerythritoltriacrylate, pentaerythritol ε-modified triacrylate, EO-modifiedglycerin triacrylate, propoxylated (3) glyceryl triacrylate, highlypropoxylated (5.5) glyceryl triacrylate, trisacryloyloxyethyl phosphate,and ε-caprolactone-modified tris(acryloxyethyl)isocyanurate.
 20. Themethod of claim 10, wherein the polymerization initiator is selectedfrom the group consisting of an alkylphenone-based photopolymerizationinitiator, acylphosphine oxide-based polymerization initiator,titanocene-based polymerization initiator, oxime ester-basedphotopolymerization initiator, or oxime ester acetate-basedphotopolymerization initiator.